U.S. patent application number 14/857944 was filed with the patent office on 2016-03-24 for light emitting device.
This patent application is currently assigned to NICHIA CORPORATION. The applicant listed for this patent is NICHIA CORPORATION. Invention is credited to Kazuto OKAMOTO, Shimpei SASAOKA.
Application Number | 20160086927 14/857944 |
Document ID | / |
Family ID | 55526459 |
Filed Date | 2016-03-24 |
United States Patent
Application |
20160086927 |
Kind Code |
A1 |
SASAOKA; Shimpei ; et
al. |
March 24, 2016 |
LIGHT EMITTING DEVICE
Abstract
A light emitting device includes a base, a first light emitting
element, a second light emitting element, and a sealing member. The
first light emitting element has an active layer of a nitride
semiconductor and has a first emission peak wavelength in a blue
region. The second light emitting element has an active layer of a
nitride semiconductor and has a second emission peak wavelength
longer than the first emission peak wavelength of the first light
emitting element. The sealing member includes a first region and a
second region. The first region contains a phosphor to be excited
by light from the first light emitting element. The first region is
provided on an element mounting surface. A first upper surface of
the first light emitting element is located in the first region.
The second region does not substantially contain the phosphor and
is provided on the first region.
Inventors: |
SASAOKA; Shimpei;
(Tokushima-shi, JP) ; OKAMOTO; Kazuto;
(Tokushima-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NICHIA CORPORATION |
Anan-shi |
|
JP |
|
|
Assignee: |
NICHIA CORPORATION
Anan-shi
JP
|
Family ID: |
55526459 |
Appl. No.: |
14/857944 |
Filed: |
September 18, 2015 |
Current U.S.
Class: |
257/89 |
Current CPC
Class: |
H01L 25/0753 20130101;
H01L 2224/16225 20130101; H01L 2924/181 20130101; H01L 2224/45144
20130101; H01L 2224/49107 20130101; H01L 2924/181 20130101; H01L
2224/45144 20130101; H01L 2224/48091 20130101; H01L 2224/48137
20130101; H01L 2224/48247 20130101; H01L 2224/48257 20130101; H01L
33/508 20130101; H01L 2224/48091 20130101; H01L 2924/00014
20130101; H01L 2924/00012 20130101; H01L 2924/00 20130101 |
International
Class: |
H01L 25/075 20060101
H01L025/075; H01L 33/52 20060101 H01L033/52; H01L 33/48 20060101
H01L033/48; H01L 33/50 20060101 H01L033/50 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 19, 2014 |
JP |
2014-191049 |
Claims
1. A light emitting device comprising: a base having an element
mounting surface; a first light emitting element having an active
layer of a nitride semiconductor and having a first emission peak
wavelength in a blue region, the first light emitting element
having a first upper surface and a first lower surface opposite to
the first upper surface and being provided on the element mounting
surface so that the first lower surface faces the element mounting
surface; a second light emitting element having an active layer of
a nitride semiconductor and having a second emission peak
wavelength longer than the first emission peak wavelength of the
first light emitting element, the second light emitting element
having a second upper surface and a second lower surface opposite
to the second upper surface and being provided on the element
mounting surface so that the second lower surface faces the element
mounting surface; and a sealing member provided on the element
mounting surface to seal the first light emitting element and the
second light emitting element, the sealing member comprising: a
first region containing a phosphor to be excited by light from the
first light emitting element, the first region being provided on
the element mounting surface, the first upper surface of the first
light emitting element being located in the first region; and a
second region which does not substantially contain the phosphor and
which is provided on the first region, the second upper surface of
the second light emitting element being located in the second
region.
2. The light emitting device according to claim 1, wherein the
active layer of the first light emitting element is located in the
first region, and wherein the active layer of the second light
emitting element is located in the second region.
3. The light emitting device according to claim 1, wherein each of
the first light emitting element and the second light emitting
element has a substrate, and wherein the substrate of the second
light emitting element is thicker than the substrate of the first
light emitting element.
4. The light emitting device according to claim 1, wherein the
first light emitting element and the second light emitting element
are provided substantially in one plane.
5. The light emitting device according to claim 1, wherein the
element mounting surface has a lower stage and an upper stage,
wherein the first light emitting element is provided on the lower
stage, and wherein the second light emitting element is provided on
the upper stage.
6. The light emitting device according to claim 1, wherein the
second emission peak wavelength of the second light emitting
element is in a green region.
7. The light emitting device according to claim 6, wherein the
phosphor has an emission peak wavelength in a red region.
8. The light emitting device according to claim 7, wherein the
phosphor comprises potassium silicofluoride activated by
manganese.
9. The light emitting device according to claim 1, wherein the
phosphor comprises yttrium aluminum garnet activated by cerium.
10. The light emitting device according to claim 2, wherein each of
the first light emitting element and the second light emitting
element has a substrate, and wherein the substrate of the second
light emitting element is thicker than the substrate of the first
light emitting element.
11. The light emitting device according to claim 10, wherein the
first light emitting element and the second light emitting element
are provided substantially in one plane.
12. The light emitting device according to claim 11, wherein the
second emission peak wavelength of the second light emitting
element is in a green region.
13. The light emitting device according to claim 12, wherein the
phosphor has an emission peak wavelength in a red region.
14. The light emitting device according to claim 13, wherein the
phosphor comprises potassium silicofluoride activated by
manganese.
15. The light emitting device according to claim 11, wherein the
phosphor comprises yttrium aluminum garnet activated by cerium.
16. The light emitting device according to claim 3, wherein the
first light emitting element and the second light emitting element
are provided substantially in one plane.
17. The light emitting device according to claim 16, wherein the
second emission peak wavelength of the second light emitting
element is in a green region.
18. The light emitting device according to claim 17, wherein the
phosphor has an emission peak wavelength in a red region.
19. The light emitting device according to claim 18, wherein the
phosphor comprises potassium silicofluoride activated by
manganese.
20. The light emitting device according to claim 17, wherein the
phosphor comprises yttrium aluminum garnet activated by cerium.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority under 35 U. S. C.
.sctn.119 to Japanese Patent Application No. 2014-191049, filed
Sep. 19, 2014. The contents of this application are incorporated
herein by reference in their entirety.
BACKGROUND
[0002] 1. Technical Field
[0003] The present disclosure relates to a light emitting
device.
[0004] 2. Discussion of the Background
[0005] For example, Japanese Unexamined Patent Application
Publication No. 2009-099715 describes a light emitting device
having a plurality of light emitting diode (LED) chips mounted on
electrodes of different heights formed on a mounting substrate
surface. Japanese Unexamined Patent Application Publication No.
2009-099715 also describes that the LED chips may be sealed with
transparent resin containing a phosphor which is excited by an
emission wavelength of the LED chip and which emits light of a
different wavelength from the emission wavelength of the LED chip,
and also that several kinds of LED chips, such as a red LED chip, a
green LED chip, a blue LED chip, a purple LED chip, and the like,
may be used in combination.
SUMMARY OF THE INVENTION
[0006] According to one aspect of the present invention, a light
emitting device includes a base, a first light emitting element, a
second light emitting element, and a sealing member. The base has
an element mounting surface. The first light emitting element has
an active layer of a nitride semiconductor and has a first emission
peak wavelength in a blue region. The first light emitting element
has a first upper surface and a first lower surface opposite to the
first upper surface and is provided on the element mounting surface
so that the first lower surface faces the element mounting surface.
The second light emitting element has an active layer of a nitride
semiconductor and has a second emission peak wavelength longer than
the first emission peak wavelength of the first light emitting
element. The second light emitting element has a second upper
surface and a second lower surface opposite to the second upper
surface and is provided on the element mounting surface so that the
second lower surface faces the element mounting surface. The
sealing member is provided on the element mounting surface to seal
the first light emitting element and the second light emitting
element. The sealing member includes a first region and a second
region. The first region contains a phosphor to be excited by light
from the first light emitting element. The first region is provided
on the element mounting surface. The first upper surface of the
first light emitting element is located in the first region. The
second region does not substantially contain the phosphor and is
provided on the first region. The second upper surface of the
second light emitting element is located in the second region.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] A more complete appreciation of the invention and many of
the attendant advantages thereof will be readily obtained as the
same becomes better understood by reference to the following
detailed description when considered in connection with the
accompanying drawings, wherein:
[0008] FIG. 1 is a schematic sectional view of a light emitting
device according to one embodiment of the present invention;
and
[0009] FIG. 2 is a schematic sectional view of a light emitting
device according to one embodiment of the present invention.
DESCRIPTION OF THE EMBODIMENTS
[0010] The embodiments will now be described with reference to the
accompanying drawings, wherein like reference numerals designate
corresponding or identical elements throughout the various
drawings.
[0011] Hereinafter, embodiments of the present invention will be
described appropriately with reference to the drawings. Note that
light emitting devices described below embody technical ideas of
the present invention, and therefore the present invention is not
limited to the embodiments described below unless otherwise
specified. Moreover, details described in one embodiment and one
Example are also applicable to another embodiment and another
Example. Furthermore, the sizes, positional relationship, and the
like of members shown in the drawings may be exaggerated for
clarity.
[0012] Hereinafter, a visible wavelength region is in a wavelength
range between 380 nm and 780 nm (both inclusive), a blue region is
in a wavelength range between 420 nm and 480 nm (both inclusive), a
green region is in a wavelength range between 500 nm and 560 nm
(both inclusive), and a red region is in a wavelength range between
610 nm and 750 nm (both inclusive).
First Embodiment
[0013] FIG. 1 is a schematic sectional view of a light emitting
device according to the first embodiment.
[0014] As shown in FIG. 1, the light emitting device 100 according
to the first embodiment is a package-type light emitting diode
adopting a top emitting (top view) type or a side emitting (side
view) type. The light emitting device 100 includes a base member 10
("a base member" is also referred to as "a base"), a first light
emitting element 20, a second light emitting element 30, and a
sealing member 40.
[0015] The base member 10 of this embodiment is a package including
lead electrodes and a molded body integrally molded with the lead
electrodes. The base member 10 has an element mounting surface 15.
The element mounting surface 15 is a bottom surface of a recess
portion of the package, more specifically is an upper surface of
the lead electrodes.
[0016] The first light emitting element 20 is provided on the
element mounting surface 15. The first light emitting element 20 is
face-up mounted. The first light emitting element 20 has an active
layer 21 made of a nitride semiconductor. The first light emitting
element 20 has an emission peak wavelength in the blue region. In
particular, the first light emitting element 20 preferably has an
emission peak wavelength in a range between 445 nm and 465 nm (both
inclusive) in terms of luminous efficiency, color mixture with
light of another light source, excitation efficiency of a phosphor,
and the like.
[0017] The second light emitting element 30 is provided on the
element mounting surface 15. The second light emitting element 30
is face-up mounted. The second light emitting element 30 has an
active layer 31 made of a nitride semiconductor. The second light
emitting element 30 has a longer emission peak wavelength than that
of the first light emitting element 20. The second light emitting
element 30 is serially connected to the first light emitting
element 20 with a wire.
[0018] The sealing member 40 is provided on the element mounting
surface 15. More specifically, the sealing member 40 is filled in
the recess portion of the package. A base material 45 of the
sealing member is light-transmissive resin. The sealing member 40
contains a phosphor 50 excited by light of the first light emitting
element 20. The sealing member 40 seals the first light emitting
element 20 and the second light emitting element 30. The sealing
member 40 includes: in order from an element mounting surface 15
side, a first region 401 where the phosphor 50 lies; and a second
region 402 where substantially no phosphor lies. The first region
401 and the second region 402 are each in the form of a layer. The
first region 401 includes: the base material 45 and the phosphor
50; or the base material 45, the phosphor 50, and a filler. The
second region 402 substantially includes: only the base material
45; or the base material 45 and the filler.
[0019] A height of an upper surface of the first light emitting
element 20 is a height in the first region 401, and a height of an
upper surface of the second light emitting element 30 is a height
in the second region 402. In this embodiment, the upper surface of
this first light emitting element 20 and the upper surface of the
second light emitting element 30 are surfaces on a light emitting
element structure (a semiconductor laminate) side. Here, "height"
refers to a distance from (a bottom of) the element mounting
surface 15.
[0020] The light emitting device 100 having such a configuration
can suppress light loss caused by diffusing and absorbing, with the
phosphor 50, light exiting from the second light emitting element
30 having a relatively long emission peak wavelength. As described
above, relatively increasing efficiency of extracting light of the
second light emitting element 30 to an outside of the device can
increase luminous efficiency of the second light emitting element
30 in a pseudo manner. This can consequently provide a light
emitting device which emits light of mixed colors of multiple
wavelengths with high luminous efficiency.
[0021] Providing the height of the upper surface of the first light
emitting element 20 as the height in the first region 401 allows
efficient emission of the phosphor 50.
[0022] Further, as shown in FIG. 1, it is preferable that a height
of the active layer 21 of the first light emitting element be a
height in the first region 401 and a height of the active layer 31
of the second light emitting element be a height in the second
region 402. Providing such a height as the height of the active
layer 31 serving as a light emission source of the second light
emitting element 30 can more suppress the light loss caused by
diffusing and absorbing, with the phosphor 50, the light exiting
from the second light emitting element 30.
[0023] As shown in FIG. 1, in the light emitting device 100, the
first light emitting element 20 has a substrate 25, and the second
light emitting element 30 has a substrate 35. The substrate 35 of
the second light emitting element 30 is thicker than the substrate
25 of the first light emitting element 20. This makes it easy to
adjust the height of the upper surface of the second light emitting
element 30 at the height in the second region 402. Moreover,
providing the relatively thick substrate 35 can improve the
luminous efficiency of the second light emitting element 30.
[0024] As shown in FIG. 1, in the light emitting device 100, the
first light emitting element 20 and the second light emitting
element 30 are provided substantially in the same plane. In the
case where the element mounting surface of the base member is a
plane, such a base member can be relatively inexpensive and allows
easy mounting of the light emitting elements.
[0025] As shown in FIG. 1, in the light emitting device 100, the
first light emitting element 20 and the second light emitting
element 30 are provided on the same lead electrode. As a result,
the first light emitting element 20 and the second light emitting
element 30 are provided at a relatively close distance from each
other, and light exiting from the first light emitting element 20
and the light exiting from the second light emitting element 30 are
easily mixed. On the other hand, the first light emitting element
20 and the second light emitting element 30 may be provided on the
corresponding separate lead electrodes. In this cases, the first
light emitting element 20 and the second light emitting element 30
are so provided as to be relatively distant from each other,
allowing suppression of light loss caused by mutual light
absorption.
[0026] The longest emission wavelength region of a general-purpose
nitride semiconductor light emitting element is a green region.
Thus, providing the emission peak wavelength of the second light
emitting element 30 in the green region is preferable since it
easily brings about the effects of the embodiment of the present
invention. In particular, the emission peak wavelength of the
second light emitting element 30, if in the green region, is
preferably in a range between 520 nm and 560 nm (both inclusive) in
terms of the luminous efficiency, color mixture with light of
another light source, and the like.
[0027] A difference in the emission peak wavelength between the
first light emitting element 20 and the second light emitting
element 30 is, for example but not limited to, 5 nm or more,
preferably 10 nm or more, more preferably 30 nm or more, and even
more preferably 50 nm or more.
[0028] The phosphor 50 preferably has an emission peak wavelength
in the red region. This makes it possible to achieve white light
emission by mixture of light exiting from the first light emitting
element 20, from the second light emitting element 30, and from the
phosphor 50. In particular, the emission peak wavelength of the
phosphor 50, if in the red region, is preferably in a range between
620 nm and 670 nm (both inclusive) in terms of luminous efficiency,
color mixture with light of another light source, and the like.
[0029] In an example illustrated, a boundary between the first
region 401 and the second region 402 is formed into a planar shape
substantially parallel to the element mounting surface 15, but its
shape is not limited thereto and may be, for example, curved or
uneven and thus may be appropriately determined depending on
distribution of the phosphor 50. For example, as a result of
distributing the phosphor 50 around the first light emitting
element 20 depending on a shape of the first light emitting element
20 or distributing the phosphor 50 along a side surface of the
second light emitting element 30 or a side wall surface of a recess
portion, the first region 401 may be formed into a protruding
shape. Moreover, the phosphor 50, in the sealing member 40, may be
so distributed as to be eccentric toward the first light emitting
element 20, that is, may be more distributed on a first light
emitting element 20 side than on a second light emitting element 30
side.
[0030] The first region 401 and the second region 402 can be
formed, in a process of forming the sealing member 40, for example,
by dropping a liquid material containing the base material 45 and
the phosphor 50 onto the element mounting surface 15 and settling
the phosphor 50 and/or by dividing the liquid material of the
sealing member 40 into a first material containing the base
material 45 and the phosphor 50 and a second material containing
the base material 45 but substantially not containing the phosphor
and then sequentially dropping them onto the element mounting
surface 15. Moreover, it is preferable that, in the process of
forming the sealing member 40, the liquid material containing the
base material 45 and the phosphor 50 be dropped at a position
avoiding an area above the second light emitting element 30, for
example, on a side of the first light emitting element 20 opposite
to the second light emitting element 30, or immediately above the
first light emitting element 20. This consequently makes it
possible to suppress or avoid presence of the phosphor 50 on the
upper surface of the second light emitting element 30. To divide
the liquid material of the sealing member 40 into two, it is
preferable that the second material be dropped on the second light
emitting element 30 side, for example, on a side of the second
light emitting element 30 opposite to the first light emitting
element 20 or immediately above the second light emitting element
30. This makes it possible to remove the phosphor 50 disposed near
the second light emitting element 30 (on the upper surface of the
second light emitting element 30 in particular). It is preferable
in terms of performance of sealing between the first region 401 and
the second region 402 that the first material and the second
material be simultaneously solidified, but the first material may
be preliminarily solidified before the dropping of the second
material. Alternatively, the first region 401 and the second region
402 can be formed by attaching the phosphor 50 onto the element
mounting surface 15 (on the first light emitting element 20 side in
particular) through, for example, a spraying method or an
electrodeposition method and then dropping the liquid material
containing the base material 45 but substantially not containing
the phosphor with part thereof impregnated in the phosphor 50 and
solidifying the liquid material
Second Embodiment
[0031] FIG. 2 is a schematic sectional view of the light emitting
device according to the second embodiment of the present
invention.
[0032] As shown in FIG. 2, the light emitting device 200 according
to the second embodiment is a light emitting diode of a chip-on
board (COB) type adopting a top emitting (top view) type or a side
emitting (side view) type. The light emitting device 200 includes a
base member 11, a first light emitting element 20, a second light
emitting element 30, and a sealing member 40.
[0033] The base member 11 of this embodiment is a wiring board
including a base material and wiring formed on this base material.
The base member 11 has an element mounting surface 16. The element
mounting surface 16 is an upper surface of the wiring board.
[0034] The first light emitting element 20 is provided on the
element mounting surface 16. The first light emitting element 20 is
flip-chip mounted. The first light emitting element 20 has an
active layer 21 made of a nitride semiconductor. The first light
emitting element 20 has an emission peak wavelength in the blue
region.
[0035] The second light emitting element 30 is provided on the
element mounting surface 16. The second light emitting element 30
is flip-chip mounted. The second light emitting element 30 has an
active layer 31 made of a nitride semiconductor. The second light
emitting element 30 has a longer emission peak wavelength than that
of the first light emitting element 20. Moreover, the substrate 35
of the second light emitting element 30 is thicker than the
substrate 25 of the first light emitting element 20. The second
light emitting element 30 is serially connected to the first light
emitting element 20 by the wiring of the wiring board. Moreover, a
terminal structure of the wiring board allows emission of only one
or both of the first light emitting element 20 and the second light
emitting element 30.
[0036] The sealing member 40 is provided on the element mounting
surface 16. More specifically, the sealing member 40 is filled
inside a frame-like projection (made of resin containing white
pigment) provided on an upper surface of the wiring board. A base
material 45 of the sealing member is light-transmissive resin. The
sealing member 40 contains a phosphor 50 excited by light of the
first light emitting element 20. The sealing member 40 seals the
first light emitting element 20 and the second light emitting
element 30. The sealing member 40 includes in order from an element
mounting surface 16 side: a first region 401 where the phosphor 50
lies; and a second region 402 where substantially no phosphor lies.
The first region 401 and the second region 402 are each in the form
of a layer. The first region 401 includes: the base material 45 and
the phosphor 50; or the base material 45, the phosphor 50, and a
filler. The second region 402 substantially includes: only the base
material 45; or the base material 45 and a filler.
[0037] A height of an upper surface of the first light emitting
element 20 is a height in the first region 401, and a height of an
upper surface of the second light emitting element 30 is a height
in the second region 402. In this embodiment, the upper surface of
the first light emitting element 20 and the upper surface of the
second light emitting element 30 are surfaces of the substrates 25
and 35. Note that "height" here refers to (a bottom of) the element
mounting surface 16.
[0038] The light emitting device 200 having such a configuration
can also be provided as a light emitting device which emits light
of mixed colors of multiple wavelengths with high luminous
efficiency while suppressing light loss caused by diffusing and
absorbing, with the phosphor 50, light exiting from the second
light emitting element 30 having a relatively long emission peak
wavelength. Moreover, providing the height of the upper surface of
the first light emitting element 20 as the height in the first
region 401 allows efficient emission of the phosphor 50.
[0039] As shown in FIG. 2, in the light emitting device 200, the
element mounting surface 16 has a lower stage 161 and an upper
stage 162. More specifically, the element mounting surface 16 has a
recess on part of a main surface, and a bottom surface of the
recess serves as the lower stage 161 and the main surface serves as
the upper stage 162. The first light emitting element 20 is
provided at the lower stage 161, and the second light emitting
element 30 is provided at the upper stage 162. This makes it easy
to adjust the height of the upper surface of the first light
emitting element 20 at the height in the first region 401 and the
height of the upper surface of the second light emitting element 30
at the height in the second region 402. A side surface of the
recess is tilted with its aperture diameter increasing upwardly
from the lower stage 161 so that the light of the first light
emitting element 20 can easily be extracted.
[0040] As shown in FIG. 2, in the light emitting device 200, a
height of the active layer 31 of the second light emitting element
30 is the height in the first region 401 but the entire substrate
35 is at the height in the second region 402. As described above,
in a case where the second light emitting element 30 is flip-chip
mounted, more than a half of the substrate 35 is preferably at the
height in the second region 402 and the entire substrate 35 is more
preferably at the height in the second region 402. As a result,
light is transmitted from the active layer 31 into the substrate 35
and further extracted from the substrate 35 via the second region
402, thereby making it easy to suppress the light loss caused by
scattering and absorbing the light with the phosphor 50.
[0041] As shown in FIG. 2, in the light emitting device 200, the
first region 401 also extends over the second light emitting
element 30 side, but the almost entire first region 401 can be
stored in the recess of the element mounting surface 16.
[0042] Hereinafter, components of the light emitting device of the
embodiment of the present invention will be described.
Base Member 10
[0043] The base member is a member serving as a housing or a seat
on which the light emitting elements are mounted. More
specifically, examples of the base member include: one formed by
integrally molding a resin molded body with lead electrodes
through, for example, transfer molding or injection molding; and
one formed by laminating and burning a ceramic green sheet with
conductive paste printed thereon. The element mounting surface of
the base member is preferably almost flat, but may be curved. As
the base member, for example, one formed into a plate-like shape or
one having a recess portion (cup part) can be used. The recess
portion may be formed by recessing the molded body or the base
material itself. Alternatively, a frame-like projection is
separately formed on an upper surface of the almost flat molded
body or base material, thus providing an inside of this projection
as the recess portion. Shapes of the recess portion in a top view
include a rectangle, a rectangle with rounded corners, a circle,
and an ellipse. A side wall surface of the recess portion is
preferably tilted (including "curved") with an aperture diameter of
the recess portion increasing upwardly from the bottom surface of
the recess portion so that the molded body can easily be separated
from the mold and also for the purpose of efficiently extracting
the light of the light emitting elements (a tilt angle is, for
example, between 95 degrees and 120 degrees (both inclusive)
relative to the bottom surface of the recess portion). A depth of
the recess portion is not specifically limited, and is, for
example, between 0.05 mm and 2 mm (both inclusive), preferably
between 0.1 mm and 1 mm (both inclusive), and more preferably
between 0.25 mm and 0.5 mm (both inclusive).
Package
[0044] A material used for the lead electrode may include metal
that can be connected to the light emitting elements to conduct
electricity. More specifically, examples of this material include
copper, aluminum, gold, silver, tungsten, iron, nickel, cobalt, and
molybdenum, and an alloy of these substances, phosphor bronze, and
a copper-iron alloy. In particular, the copper alloy primarily
containing copper is preferable. Moreover, provided on its surface
layer may be plating of, for example, silver, aluminum, rhodium,
gold, copper, or an alloy of these substances, or a light
reflective layer, among which the silver having good light
reflectivity is preferable. The lead electrode has, for example, a
lead frame divided into a separate individual piece as part of the
individual light emitting device through cut-forming. The lead
frame has a base material obtained by performing various processing
such as pressing, etching, and rolling on a metal plate formed of
the aforementioned material. A thickness of the lead electrode can
be selected arbitrarily, for example, between 0.1 mm and 1 mm (both
inclusive), and preferably between 0.2 mm and 0.4 mm (both
inclusive).
[0045] The molded body is integrally molded with the lead
electrodes, forming the package. The molded body is a solidified
substance primarily of white or black resin. Examples of a base
material of the molded body include: thermoplastic resin such as
polyamide resin, polyethylene terephthalate, polycyclohexane
terephthalate, liquid crystal polymer, and polycarbonate resin; and
thermosetting resin such as polybismaleimide-triazine resin, epoxy
resin, modified epoxy resin, silicone resin, modified silicone
resin, and polyimide resin. These base materials can contain as a
filler or coloring pigment, particles or fibers of, for example,
glass, silica, titanium oxide, magnesium oxide, magnesium
carbonate, magnesium hydroxide, calcium carbonate, calcium
hydroxide, calcium silicate, magnesium silicate, wollastonite,
mica, zinc oxide, barium titanate, potassium titanate, aluminum
borate, aluminum oxide, zinc oxide, silicon carbide, antimony
oxide, zinc stannate, zinc borate, iron oxide, chromium oxide,
manganese oxide, and carbon black.
Wiring Board
[0046] A base material of the wiring board preferably has
electrical insulation properties, but even one with electrical
conductivity can be electrically insulated from the wiring with an
insulation film or the like interposed therebetween. Examples of a
material of the base material of the wiring board include: ceramics
containing aluminum oxide, aluminum nitride, and a mixture of these
substances; metal containing copper, iron, nickel, chrome,
aluminum, silver, gold, titanium, and an alloy of these substances;
resin such as epoxy resin, BT resin, and polyimide resin, and fiber
reinforced resin of these resin (e.g. glass for reinforced
material). The wiring board can be provided as a rigid board or a
flexible board, depending on the material and the thickness of the
base material. Moreover, the wiring board is not limited to a
flat-plate-like form, but can be in a form having a recess portion
as is the case with the aforementioned package.
Wiring
[0047] The wiring is formed on at least an upper surface of the
base material, and may also be formed on an inside, a lower
surface, and a side surface of the base material. Moreover, the
wiring may have a land (die pad) part coupled to the light emitting
elements, a terminal part for external connection, a lead-out
wiring part for connecting them together, and the like. Examples of
a material of the wiring include copper, nickel, palladium,
rhodium, tungsten, chrome, titanium, aluminum, silver, gold, and an
alloy of these substances. In particular, the copper or a copper
alloy is preferable in terms of heat radiation performance.
Moreover, provided on its surface layer may be a plating or a light
reflective film of silver, aluminum, rhodium, gold, copper, or an
alloy of these substances, among which the silver having excellent
light reflectivity is preferable. These wiring can be formed
through, for example, electrolytic plating, non-electrolytic
plating, spattering, vapor deposition, printing, application,
co-firing, or a post-firing method.
Light Emitting Element, First Light Emitting Element 20, and Second
Light Emitting Element 30
[0048] For the light emitting elements, a semiconductor light
emitting element such as an LED element can be used. The light
emitting element includes at least a light emitting element
structure, and further includes a substrate in many cases. A shape
of the light emitting element in a top view is preferably a
rectangle, and in particular a square or a rectangle elongated in
one direction, but a different shape may be used. A side surface of
the light emitting element (substrate in particular) may be
substantially perpendicular to the upper surface or may inwardly or
outwardly tilt. The light emitting element may have a structure
having both a p-electrode and a n-electrode on the same surface
side or a counter electrode (upper-and-lower electrode) structure
in which the p-electrode and the n-electrode are provided
separately on the upper surface and the lower surface of the
element. The light emitting element with the structure having both
the p-electrode and the n-electrode on the same surface side has
each of the electrodes connected to the lead electrode or the
wiring with a wire (face-up mounting) or has each electrode
connected to the lead electrode or the wiring with a conductive
bonding agent (flip-chip (face-down) mounting). The light emitting
element with the counter electrode structure has the lower
electrode connected to the lead electrode or the wiring with the
conductive bonding agent, and has the upper electrode connected to
the lead electrode and the wiring with a wire. The number of light
emitting elements mounted in one light emitting device may be at
least two, and two or more kinds of semiconductor light emitting
elements may be combined together. The plurality of light emitting
elements can be connected in series or in parallel to each
other.
Substrates 25, 35
[0049] The substrate may be a substrate for crystal growth capable
of growing a crystal of a semiconductor forming the light emitting
element structure or a coupling substrate to be coupled to the
light emitting element structure separated from the substrate for
crystal growth. If the substrate has light transmissivity, the
flip-chip mounting can easily be adopted and light extraction
efficiency can easily be improved. If the substrate has electrical
conductivity, the counter electrode structure can be adopted, and
also power efficiency can easily be improved because it is easy to
perform uniform in-plane power feeding to the light emitting
element structure. Examples of a base material of the substrate for
crystal growth include sapphire, spinel, gallium nitride, aluminum
nitride, silicon, silicon carbide, gallium arsenic, gallium
phosphide, indium phosphide, zinc sulfide, zinc oxide, zinc
selenide, and diamond. As the coupling substrate, a light-blocking
substrate is preferable. The light-blocking substrate is excellent
in heat conductivity in many cases, and easily improves heat
radiation performance of the light emitting element. More
specifically, examples of material used for the light-blocking
substrate include silicon, silicon carbide, aluminum nitride,
copper, copper-tungsten, gallium arsenic, and ceramics. If the
substrate is the coupling substrate, presence of a coupling layer
(reflection layer) which suppresses traveling of light from the
light emitting element structure into the substrate permits
substrate selection, putting more priority to the heat conductivity
and the electrical conductivity than optical characteristics. A
thickness of the substrate is, for example, between 50 .mu.m and
1000 .mu.m (both inclusive), and preferably between 100 .mu.m and
500 .mu.m (both inclusive) in view of mechanical strength of the
substrate and a thickness of the entire light emitting device. On
the other hand, if the substrate has light transmissivity, a
greater thickness is better in terms of luminous efficiency, more
preferably between 200 .mu.m and 900 .mu.m (both inclusive), and
even more preferably between 300 m and 900 .mu.m (both
inclusive).
Light Emitting Element Structure, Active Layers 21 and 31
[0050] The light emitting element structure contains a laminated
body of semiconductor layers, that is, at least an n-type
semiconductor layer and a p-type semiconductor layer, and
preferably has an active layer therebetween. Further, the light
emitting element structure may include an electrode and a
protective film. The electrode can be formed of gold, silver, tin,
platinum, rhodium, titanium, aluminum, tungsten, palladium, nickel,
or an alloy of these substances. The protective film can be
composed of oxide or nitride of at least one kind of element
selected from the group consisting of silicone, titanium,
zirconium, niobium, tantalum, and aluminum. An emission wavelength
of the light emitting element structure can be selected from an
ultraviolet region to an infrared region, depending on a material
of the semiconductor and a ratio of its mixed crystal. A material
used for the semiconductor preferably includes a nitride
semiconductor, i.e. a material which permits emission of light of a
short wavelength and which is capable of efficiently exciting the
phosphor (mainly expressed as general expression
In.sub.xAl.sub.yGa.sub.1-x-yN, 0.ltoreq.x, 0.ltoreq.y,
x+y.ltoreq.1). Alternatively, for example, an InAlGaAs
semiconductor, an InAlGaP semiconductor, zinc sulfide, zinc
selenide, or silicone carbide can be used.
Sealing Member 40, Base Material 45
[0051] The sealing member is a member which seals, for example, the
light emitting element to protect it from dust, external force, and
the like. The sealing member preferably has electrical insulation
properties. Moreover, the sealing member preferably permits
transmission of light exiting from the light emitting element
therethrough (preferably with a light transmittance of 70% or
more). Examples of the base material of the sealing member include
silicone resin, epoxy resin, phenol resin, polycarbonate resin,
acrylic resin, TPX resin, polynorbornene resin, modified resin of
these resin, and hybrid resin containing at least one of these
kinds of resin. It may also be glass. Of these substances, the
silicone resin or its modified resin is preferable since it is
excellent in heat resistance and light resistance and has less
volume shrinkage after hardening. In particular, the base material
of the sealing member preferably primarily contains phenyl silicone
resin. The phenyl silicone resin also has excellent gas barrier
properties and easily suppresses deterioration in the lead
electrode and the wiring caused by corrosive gas. The sealing
member contains a phosphor in its base material. The sealing member
preferably contains a filler and the like in its base material, but
does not necessarily have to contain them.
Filler
[0052] As the filler, for example, a diffusing agent or a coloring
agent can be used. More specifically, examples of the filler
include silica, titanium oxide, magnesium oxide, magnesium
carbonate, magnesium hydroxide, calcium carbonate, calcium
hydroxide, calcium silicate, zinc oxide, barium titanate, aluminum
oxide, iron oxide, chrome oxide, manganese oxide, glass, and carbon
black. The filler has, for example, a spherical shape, an unstable
granular shape, a needle-like shape, a columnar shape, a plate-like
shape (including a scaly shape), a fibrous form, and an arborized
(dendritic) shape. It may be hollow or porous.
Phosphor 50
[0053] The phosphor absorbs at least part of primary light exiting
from the light emitting element and emanates secondary light of a
different wavelength from that of the primary light. The phosphor
may be composed of one kind or two or more kinds in combination.
More specifically, examples of the phosphor include yttrium
aluminum garnet activated by cerium, nitrogen-containing
aluminocalcium silicate activated by europium and/or chrome, sialon
activated by europium, silicate activated by europium, and
potassium silicofluoride activated by manganese. Of these
substances, the potassium silicofluoride activated by manganese is
a phosphor with an emission peak wavelength in a red region, has a
relatively narrow emission spectral line width, and is preferable
for, for example, improving color reproducibility of a liquid
crystal display.
Bonding Agent
[0054] The bonding agent is a member bonding the light emitting
element to the base member. Examples of a material of an insulating
bonding agent include epoxy resin, silicone resin, polyimide resin,
and modified resin and hybrid resin of these resin. Examples of a
material of an electrically-conducting bonding agent include an
electrically-conducting paste of, for example, silver, gold, or
palladium, or tin-bismuth-based, tin-copper-based,
tin-silver-based, or gold-tin-based solder.
Wire
[0055] The wire is a conductive wire connecting together the
electrode of the light emitting element and the lead electrode and
the wiring. More specifically, a metal wire of gold, copper,
silver, platinum, aluminum, or an alloy of these substances can be
used. In particular, a gold wire in which fractures due to stress
from the sealing member hardly occurs and which has excellent
thermal resistance is preferable. Moreover, for the purpose of
improving light reflectivity, at least a surface thereof may be
formed of silver or a silver alloy.
EXAMPLES
[0056] Hereinafter, Examples according to the embodiment of the
present invention will be described in detail. It is needless to
say that the present invention is not limited to Examples described
below.
First Example
[0057] A light emitting device of Example 1 is an SMD-type LED of a
substantially rectangular solid shape which adopts the top view
type and which has the structure of the light emitting device 100
in the example shown in FIG. 1.
[0058] A base member is a package which is 2.00 mm by 4.0 mm in
size, which is of 1.2 mm in thickness, and which is formed by
integrally molding a resin molded body with a pair of positive and
negative lead electrodes. This package is manufactured by
installing, in a mold, a machined metal plate (lead frame) formed
of pairs of lead electrodes continuously and vertically and
horizontally lying with a suspension lead in between, injecting a
liquid constituent material of the resin molded body, solidifying
it and separating it from the mold, and then cutting it (dividing
it into individual pieces).
[0059] Each of the two lead electrodes is a plate-like small piece
of a copper alloy of 0.2 mm in maximum thickness with its surface
provided with silver plating. An exposed region of a lower surface
of the two lead electrodes is substantially flush with a lower
surface of the resin molded body, forming a lower surface of the
package. Each of the two lead electrodes has a cut suspension lead
part exposed on an end surface of the package (resin molded
body).
[0060] The resin molded body has a rectangular shape so outlined as
to be 2.0 mm by 4.0 mm in a top view with a maximum thickness of
1.2 mm, and is formed of epoxy resin containing silica and titanium
oxide. Formed on an upper surface of the resin molded body, that
is, a substantially central area of the upper surface of the
package is a recess portion having a depth of 1.0 mm with an
aperture of a rectangular shape which has round corners in a top
view and which is 1.4 mm by 3.4 mm A side wall surface of the
recess portion is a tilted surface forming an angle of 111.3
degrees with a bottom surface of the recess portion.
[0061] Two light emitting elements are bonded at their substrate
sides to the upper surface of the negative lead electrode formed on
the bottom surface of the recess portion of the package (an element
mounting surface) with a bonding agent of dimethyl silicone resin
(of several micrometers in thickness). The first light emitting
element is an LED element in which a light emitting element
structure (of approximately 10 .mu.m in thickness) containing an
active layer made of a nitride semiconductor is laminated on a
sapphire substrate (of 150 .mu.m in thickness), which is capable of
emitting blue light (with an emission peak wavelength of
approximately 453 nm), and which is shaped into a rectangle of 550
.mu.m by 750 .mu.m in size in a top view. The second light emitting
element is an LED element in which a light emitting element
structure (of approximately 10 .mu.M in thickness) containing an
active layer of a nitride semiconductor is laminated on a sapphire
substrate (of 800 .mu.m in thickness), which is capable of emitting
green light (with an emission peak wavelength of approximately 555
nm), and which is shaped into a rectangle of 550 .mu.m by 750 .mu.m
in size in a top view. The first light emitting device has an
n-electrode connected to the upper surface of the negative-side
lead electrode with a wire and has a p-electrode connected to an
n-electrode of the second light emitting element with a wire. The
second light emitting element has a p-electrode connected to the
upper surface of the positive-side lead electrode with a wire. The
wire is a gold wire of 25 .mu.m in diameter.
[0062] A sealing member, with which the recess portion of the
package is filled, coats the two light emitting elements. The
sealing member has phenyl silicone resin as a base member, and
contains therein a phosphor (with an emission peak wavelength of
approximately 630 nm) of potassium silicate fluoride activated by
manganese and a filler of silica. The phosphor is
eccentrically-located on a lower side (bottom surface of the recess
portion) in the sealing member by settling. A thickness of a lower
region (first region) where this phosphor lies is 600 .mu.m, and a
thickness of an upper region (second region) where substantially no
phosphor lies is 400 .mu.m. The upper surface of the sealing member
is substantially flush with the upper surface of the package and
substantially flat-surfaced (in a precise sense, a surface slightly
recessed due to cure shrinkage). This sealing member is formed by
dropping a liquid constituent material into the recess portion of
the package with, for example, a dispenser, and then heating and
solidifying it.
[0063] The light emitting device of Example 1 configured as
described above can provide the same effects as those of the light
emitting device 100 according to the first embodiment.
[0064] The embodiment of the present invention refers to a light
emitting device including: a base member having an element mounting
surface; a first light emitting element being provided on the
element mounting surface, having an active layer of a nitride
semiconductor, and having an emission peak wavelength in a blue
region; a second light emitting element being provided on the
element mounting surface, having an active layer of a nitride
semiconductor, and having a longer emission peak wavelength than
the emission peak wavelength of the first light emitting element;
and a sealing member being provided on the element mounting
surface, containing a phosphor excited by light of the first light
emitting element, and sealing the first light emitting element and
the second light emitting element, wherein the sealing member
contains, in order from a side of the element mounting surface, a
first region where the phosphor lies and a second region where the
phosphor does not substantially lie, a height of an upper surface
of the first light emitting element is a height in the first
region, and a height of an upper surface of the second light
emitting element is a height in the second region.
[0065] The embodiment of the present invention can provide a light
emitting device which emits light of mixed colors of multiple
wavelengths with high luminous efficiency while suppressing light
loss of a nitride semiconductor light emitting element having a
relatively long emission peak wavelength.
[0066] Obviously, numerous modifications and variations of the
present invention are possible in light of the above teachings. It
is therefore to be understood that within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described herein.
* * * * *